RuningValue not working to give Cumulative Stacked Chart

I have a dataset that is showing the correct data, but putting it into a stacked bar chart and using the RunningValue function to try and plot it cumulatively is giving numbers that start way higher than they should.

My data is aggregated at the database, giving a dataset of:

• Date of data
• Count
• Sum of Value
• Filter Item 1
• Time Since Date
• Stacking Category
• 5 other fields

I am plotting with Time Since X along the X axis, Stacking Category is my Series fiel开发者_如何学Pythond (there are 4 possible options), and my Y is using this function:

=RunningValue(IIF(Parameters!VolumeOrValue.Value="Volume",
 Fields!Count.Value,
 Fields!SumValue.Value),Sum,Nothing)

This should show me in the first X bar only 1 of the series, with a count as 1, or value of 100. Instead I get 3 of the series, with Counts summed up to 2500, which is more than the total sum of all of the count fields.

Can anyone point me to where my problem is?

Edit: Setting the CategoryField in the Series Properties dialog to match the Catgory that is set for the chart means that each bar is increasing by the right amount, but each stacked slice starts at the size of the entire value of the last bar. I need to get the reset to work properly, but I can't set any "Groupings" as normally recommended, and choosing any field name or Series name causes an error.

I managed to get it working quite simply...

Clicking on the Field on the right hand side of the chart on the Drop Series Fields Here section has a Group properties which when expanded has a name of the grouping. Plugging this into the RunningValue function as the last argument got it working properly (after removing the CategoryField setting).